1. Field of the Invention
The present invention relates to a continuous medium folding device, and particularly relates to a continuous medium folding device for folding a printed continuous medium along transversal perforations using a swing arm such that the continuous medium is accordion-folded.
2. Description of the Related Art
Among various types of printers such as an electrophotographic printer, a continuous medium printing device is known as a printer which can print marks on a continuous medium.
The continuous medium printing device includes a hopper where the continuous medium is stored and a stacker in which the continuous medium is received. The continuous medium printing device pulls out the continuous medium from a stacker, prints marks on the continuous medium and accommodates the printed continuous medium in the stacker. The above-described continuous medium folding device is provided at the stacker. The swing arm swings right and left such that the printed continuous medium is accordion-folded along transversal perforations.
Recently, there is a need for a higher throughput for a printing operation. In order to meet such a need, it is required to increase a transportation speed of the continuous medium. Thus, it is required to operate the swing arm at an increased swinging rate.
On the other hand, the continuous medium to be printed may be provided in various thicknesses depending on the use. For example, it may be required to send the continuous medium separated at transverse perforations using a postal service. In such a case, in order to reduce the weight of the postal matter, the continuous medium must have reduced thickness. However, it is known that the stiffness of the continuous medium reduces as the thickness of the continuous medium is reduced. Thus, since the continuous medium with reduced thickness easily bends during the folding operation, a high reliability folding cannot be guaranteed. This is particularly the case where the processing speed of the device is increased.
Accordingly, there is a need for a continuous medium folding device which can securely fold continuous medium of reduced thickness while the swing arm is operated at a high swinging rate.
FIG. 1 is a schematic diagram showing a continuous medium folding device 10 of the related art. The continuous device 10 includes a continuous medium swaying mechanism 30 provided at a central position above a stacker table 20 and continuous medium fold-line pressing mechanisms 40 and 50 provided at an X2_side and X1-side, respectively, above the stacker table 20.
The continuous medium swaying mechanism 30 includes a hollow swing arm 31 through which a continuous medium 1 is guided and a swing mechanism (not shown) for swinging the swing arm 31 in A1- and A2-directions.
The continuous medium fold-line pressing mechanism 40 includes a flap 41 and a mechanism (not shown) for pivoting the flap 41 in B1- and B2-directions in a reciprocating manner. The continuous medium fold-line pressing mechanism 50 includes a flap 51 and a mechanism (not shown) for pivoting the flap 51 in B1- and B2-directions in a reciprocating manner.
The swing arm 31 swings in the A1- and A2-directions about an axis 32 at a rate corresponding to a feeding speed of the continuous medium 1 fed in a direction shown by an arrow Z2. The swing arm 31 uses its tip part 31a to support and direct the continuous medium 1 towards the table 20 and sway the continuous medium 1 alternately in the X1- and X2- directions. In this manner, the continuous medium 1 is folded at a constant width. The flaps 41 and 51 are pivoted alternately in synchronous with the swinging rate of the swing arm 31, so as to press the fold lines 12 and 13 of the continuous medium 1.
Accordingly, the continuous medium 1 is folded along the transverse perforations 4 into an accordion-like configuration and is received on the stacker table 20. Reference 5 represents an accordion-folded continuous medium which is received on the stacker table 20.
When the swing arm 31 swings in A1-A2 directions and the continuous medium 1 is swayed, a higher pressure is produced on the front side of the continuous medium 1 and a lower pressure is produced on the back side. The terms “front” and “back” are defined in the direction of sway of the continuous medium 1. The difference in the front-side pressure and the back-side pressure causes a bending force of the continuous medium 1.
When the continuous medium 1 of thin sheets is used, the stiffness of sheet is small. Therefore, the above-described bending force becomes greater than the stiffness of the sheets. Thus, the continuous medium 1 will be bent as shown by reference 15 and will not be folded normally. This may cause an unacceptably bad folding.
A trajectory 300 of a tip part 31a of the swing arm 31 becomes an arc of a circle centered on the axis 32. Therefore, particularly, when the swing arm 31 is swayed through to the right and left end positions, the tip part 31a leaves the top surface 6 of the stacked continuous medium 5 and the length of the continuous medium 1 protruding from the tip part 31a of the swing arm 31 becomes greatest. Therefore, the bend 15 of the continuous medium 1 may occur when the swing arm 31 is swayed and reaches near the right or left end positions.
In order to prevent the occurrence of the bend 15 of the continuous medium, it is desirable to minimize the distance between the tip of the swing arm 31 and the top surface 6 of the stacked continuous medium 5.